1. Field of the Invention
The invention relates to a flexible heat-insulated conduit made up of at least one medium-carrying internal tube, an external tube surrounding the at least one internal tube, and a heat-insulating layer based on polyurethane foam or polyisocyanurate foam and located between the at least one internal tube and the external tube and to a method for manufacturing a heat-insulated conduit.
2. Description of the Background Art
EP 0 897 788 B1 discloses a heat-insulated conduit that comprises one or more internal tubes, a heat-insulating layer surrounding the internal tube or tubes, and a plastic external tube. In order to improve flexibility, the external tube is equipped with a slight corrugation. The heat-insulating layer is made of polyurethane foam that is made of a mixture of polyol and isocyanate, which is introduced into the gap between the internal tube or tubes and the external tube, and foams up therein.
The manufacture of polyurethane foam is the subject matter of EPÜ 1 371 469 B1. The mixture to be introduced into the gap is manufactured by delivering polyol, a propellant, and air to a static mixer, mixing them therein, and mixing this mixture with isocyanate in a dynamic mixer. The mixture manufactured in this fashion is introduced into the gap between the internal tube or tubes, where it foams up.
Although the corrugation of the external tube as well as all the materials, such as plastic, used for the internal tube or tubes and the external tube, make the conduit relatively flexible, the conduit is impossible to use in many cases.
The heat-insulated conduit manufactured in accordance with the documents described is utilized preferably as a house connector line for supplying district heat. It often happens in this context that the conduit must be curved around tight radii in order, for example, to get around structures, trees requiring protection, etc.
It is additionally desirable to wind the conduit onto drums having a small drum core diameter, and to transport it thereon to the installation site.